The storm is forecast to strengthen over the next few days and could threaten the Carolinas at the weekend with heavy rain and 70 miles per hourwinds, just below hurricane force, according to the National Hurricane Center.

Forecast models predict it brushing the Outer Banks before heading towards the New York-New Jersey coast early next week.

Heavy rain over the northern Appalachians and New England over the next two to three days could greatly enhance the potential for Joaquin to cause flooding if it comes ashore, forecasters at the privately-run Weather Underground said.

Joaquin was the tenth named storm of the 2015 Atlantic hurricane season after forming east of the Bahamas late Monday. It was located about 425 miles (680 km) east-northeast of the northwestern Bahamas on Tuesday, with maximum sustained winds of 45 mph (73 kph), the Miami-based NHC said.

Joaquin is moving toward the west at 5 mph, the NHC said, with tropical storm force winds extending 70 miles from the center, NHC said.

The NHC warned that its wind speed predictions for Joaquin may be conservative, and "some of the guidance suggests that Joaquin could become a hurricane in a few days."

A U.S. Air Force plane was being sent to investigate Joaquin on Tuesday to try and obtain a better estimate of its intensity, the NHC said.

The government's annual forecast predicted a quieter-than-normal 2015 Atlantic hurricane season, with six to 10 named storms and up to four reaching hurricane status of 74 mph.

So far only two hurricanes have formed, Danny and Fred, which both ran out of steam while still far out at sea.

Among the factors in this year's predicted weaker hurricane season is the El Niño weather phenomenon, the warming of Pacific waters that affects wind circulation patterns and makes the formation of hurricanes in the Atlantic-Caribbean basin less likely.